The present invention relates, in general, to aerial tramways, and more particularly, relates to the detachable and permanent grip assemblies used to secure the passenger conveying units of an aerial tramway to the haul rope.
Two general categories of aerial tramway haul rope grip assemblies are in widespread use, namely, detachable grip assemblies and permanently affixed grip assemblies. Detachable grip assemblies are employed in aerial tramways such as gondolas, some chairlifts and some trams. Detachable grip assemblies are regularly removed from the tramway haul rope, usually to permit loading and unloading of the passenger carrier units at a tramway terminal or station. The permanently affixed grip assemblies are used in aerial tramways such as chairlifts, ski lifts, Poma lifts and trams. While such "permanent" grips can be removed from the haul rope, they seldom are removed unless they are undergoing maintenance or repair. As used herein, the expression "aerial tramway" shall be understood to include any haul rope based conveying system of the type having a plurality of load carrying units secured to a haul rope to enable the units to be conveyed over or along a course.
The performance criteria for aerial tramway grip assemblies typically have been established by industry regulating bodies or the laws of various countries. In the United States, for example, the current grip performance criteria is that the gripping force generated by the grip assembly must be at least three times that required to prevent slippage of the grip along the rope (a safety factor of 3), and the grip must produce a three percent reduction in rope area at the grip. Since rope manufacturers typically manufacture haul rope to a nominal diameter plus 6% minus 3% along the rope length, grip assemblies must be capable of meeting these performance criteria notwithstanding variation of the rope diameter along the length of the rope.
Prior art aerial tramway grip assemblies have been formed with at least one movable clamping jaw which cooperates with a second fixed or movable jaw to grip the haul rope therebetween. Some systems have further included opposed wedging surfaces in the clamping jaws, but such wedging surfaces have been generally horizontally oriented which results in the weight of the passenger carrier unit tending to pull the haul rope out of the gripping jaws. The prior art wedging jaw-based systems, therefore, have not been fail-safe, and they have attained the very substantial rope gripping forces required almost entirely as a result of spring or fastener generated forces urging the two jaws together.
In recent years there also has been a trend in the aerial tramway industry to increase the uphill carrying capacity of tramways. This, in turn, has resulted in an increase in prime mover horsepower and a corresponding increase in haul rope diameter. Carrier units also have increased in capacity and accordingly weight. Thus, the rope gripping forces are now quite substantial, and the problems attendent to detaching and attaching the carrier units from the rope are substantial. A gondola system may require, for example, 5000-6000 pounds of force to open the detachable grip assembly.
To solve the substantial gripping problems which have developed over the years in aerial tramways, detachable grip assemblies have become relatively complex. Many grips have over 100 parts and require involved support structures at the tramway terminals to operate the grips. Moreover, the grip release levers often pose problems in terms of supporting the haul rope on towers intermediate the stations, namely, the release levers can interfere with attempts to hold down the haul rope at towers at which hold down sheaves would normally be required.